Osmotic Pressure Calculation Formula


The pressure that must be applied to a more concentrated solution to prevent the flow of pure solvent into the solution separated by a semipermeable membrane is called the osmotic pressure. This relationship can be expressed as follows:

PV = nRT

Where,

  • P = is the pressure (atm),
  • V = is the volume (L),
  • N = is number of moles of solute,
  • R = is the gas constant (0.082 L atm/mol deg), and
  • T = is the absolute temperature (°C).


Example:

What is the osmotic pressure of 50 g dextrose in 1,000 mL of water at room temperature (25°C)?

P = [(0.28)(0.082)(298)]/(1) 

= 6.84 atm


Where,

  • n = (50 g dextrose)/(MW of 180) = 0.28 mol of dextrose,
  • T = 273°C + 25°C = 298°C
  • V = 1 L
  • R = 0.082 L atm/mol deg


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